1. Field of the Invention
The present invention relates to a solid-state image sensor and an image pickup apparatus.
2. Description of the Related Art
A CMOS solid-state image sensor has been widely used for an image pickup apparatus such as a digital still camera or digital video camera. In recent years, there has been proposed a configuration for implementing a global shutter function of making the accumulation times of respective pixels of a CMOS solid-state image sensor equal to each other (performing exposure for the same time).
In a configuration described in Japanese Patent Laid-Open No. 2004-111590, for example, a charge holding portion for holding signal charges generated by the photoelectric conversion portion of each pixel is provided for each pixel. In this configuration, the photoelectric conversion portions of all the pixels simultaneously start exposure and accumulation. Upon completion of accumulation, the signal charges of the photoelectric conversion portions of all the pixels are simultaneously transferred to the corresponding charge holding portions, respectively. It is possible to obtain an image pickup signal, for which the accumulation periods of all the pixels are equal to each other, by sequentially reading out pixel signals based on the signal charges held in the charge holding portions from a common output line.
Furthermore, in a configuration described in Japanese Patent Laid-Open No. 2006-246450, it is possible to transfer some of charges generated by a photoelectric conversion portion to a charge holding portion during part of an exposure period.
In general, a charge hold portion is covered by a light-shielding member, thereby preventing extraneous light from entering. Since, however, it is difficult to completely prevent extraneous light from entering, some light leaking from the light-shielding member may enter the charge holding portion. In this case, charges are generated within the charge holding portion due to the leakage light. These charges are noise charges different from signal charges generated by a photoelectric conversion portion during an accumulation period. These noise charges vary depending on the time during which the leakage light is incident on the charge holding portion and the intensity of the light, and appear as shading or an afterimage in an output image, thereby causing deterioration in image quality.
The configurations described in Japanese Patent Laid-Open Nos. 2004-111590 and 2006-246450, however, do not consider reducing the leakage light into the charge holding portion.